The present invention relates to a method for calibrating a microwave source. It can notably be applied to the phase calibration of the elementary sources of an array antenna.
An array antenna comprises an array of phase-controlled elementary sources, each source being connected to a radiating element. By controlling the phases of the elementary sources in a suitable manner, a plane wave can be created in a desired direction. An electronic sweep can thus be carried out, in other words the direction of the main lobe can be modified by controlling the phases of the various sources.
However, elementary sources can go out of adjustment, producing a different phase from the setpoint phase. These phase differences lead to limitations in the performance of the sweep. They can notably result in a reduction in gain of the antenna, a distortion of the main lobe, an increase in the level of the secondary lobes and a deviation of the electromagnetic axis.
A known solution is to carry out periodic calibrations of the phase of each elementary source. In order to perform a calibration of an elementary source:    a calibration circuit is closed, the calibration circuit comprising an injection channel connected to a measurement channel via the source to be calibrated;    a test signal is injected through the source to be calibrated, the test signal being injected on the injection channel,    the phase φm of the signal having passed through the source to be calibrated is measured, the phase of the signal being measured on the measurement channel.
However, microwave interference exists that causes errors in the phase measurements of each elementary source.